1. Field of the Invention
The present invention generally relates to the delivery of secondary fuel for combustion in kilns and the like, and more specifically to an apparatus for projecting fuel through an end inlet of the kiln comprising oppositely rotating rollers.
2. Description of the Related Art
It is desirable in many applications to supplement or replace conventional oil, gas, or coal fuels to obtain savings in the total fuel costs of operation or reduce emissions of the combustion process. It is well known to use scrap or worn rubber pneumatic tires from motor vehicles as secondary or alternative fuel in a furnace or kiln. The scrap tires provide a relatively inexpensive source of fuel that has typically in the past been discarded in land fills. For example, cement kilns can effectively be fired using scrap tires as a significant portion of the total fuel without the ash diminishing the quality of the cement. It will be noted that other furnaces or kilns, such as lime kilns, and other fuels, such as wood chips, can produce similar results.
Various attempts have been made in the art to provide an apparatus to supply tires as a secondary fuel. For example, U.S. Pat. No. 4,551,051 discloses a lock chamber structure attached to an end wall of a kiln having a runway and two gates. The runway is downwardly inclined toward the kiln. The first or receiving gate is provided with a tire holder for holding a whole tire in a rolling position in which it is aligned with the runway. When the tire is loaded into the tire holder, the receiving gate is closed and the second or kiln gate is opened. Once the kiln gate is opened, the tire is released by the tire holder and accelerates down the runway and continues to roll into the kiln. An apparatus of this type may not deliver the tire an adequate distance into the kiln. The tire must be delivered a distance to provide ample time to burn and complete all necessary chemical reactions. This is especially true for reinforcing fiber or steel wire embedded in the rubber tires to be properly absorbed into the cement mixture.
U.S. Pat. No. 5,078,594 discloses an apparatus for supplying tires through a port in the cylindrical wall of an operating rotating kiln. The apparatus includes a closure assembly for the port, a drop tube, a stationary staging assembly, and a kiln mounted transfer assembly. A tire is loaded on the staging assembly and as the kiln rotates the transfer assembly sweeps past and picks up the tire. As the transfer assembly reaches near vertical position the tire moves under the force of gravity toward the port. The port closure assembly is automatically cammed to an opened-position, and the tire drops through the port and drop tube into the kiln. As the kiln continues to rotate the spring loaded closure assembly automatically returns to a closed-position. An apparatus of this type requires a port hole in the cylindrical wall of the kiln and a closure assembly and thus requires modifications to the kiln or a specially designed kiln. Additionally, the use of whole tires may not give a good distribution of the secondary fuel into the cement mixture.
It is also known in the art to chop or shred tires for fuel which is commonly referred to as tire-derived fuel (TDF). TDF typically is composed of variously-sized pieces including coarse pieces and various amounts of reinforcing fiber and steel wire. Various attempts have been made in the prior art to supply TDF to a kiln or furnace. For example, U.S. Pat. No. 4,806,056 discloses an apparatus for delivering TDF to a combustion chamber of a kiln through an end wall. The apparatus includes a hopper having a variable speed screw conveyor, an electric blower, a nozzle assembly, and a delivery conduit. The screw conveyor delivers a metered amount of tire pieces from the hopper in response to the required firing rate of the kiln. An exhaust pipe from the blower is connected to a nozzle. A shroud encloses the nozzle and includes an inlet through which the tire pieces are introduced. The tire pieces are entrained by the flow of air carrying them into the delivery conduit for delivery to the kiln. An apparatus of this type may introduce an excessive amount of air into the kiln and thereby create a cooling effect in the kiln. Additionally, the apparatus may not deliver the tire an adequate distance into the kiln to provide the time required for completion of all the necessary chemical reactions. Moreover, the coarse pieces of fuel may easily jam or clog the apparatus requiring it to be shut down and cleared of the clogged fuel pieces.
See also U.S. Pat. No. 4,984,983 an apparatus for ballistically introducing whole drums or smaller containers from an end of the kiln and an apparatus for pneumatically injecting a granular product from an end of the kiln.
U.K. Patent No. 253,905 discloses an apparatus for feeding pulverized fuel into a combustion chamber of a boiler furnace. The apparatus comprises two drums rotating in opposite directions, a hopper, and a feeding mechanism. Pulverized coal from the discharge hopper is fed by the feeding mechanism between the drums. The drums deliver a thin sheet of the fuel through a nozzle in a horizontal direction and into the updraft of the combustion chamber. An apparatus of this type may require the fuel to be pulverized and would jam or clog upon the introduction of coarse pieces of fuel. Additionally, the apparatus may require a feeding mechanism in the input hopper to prevent clogging or jamming of the pulverized fuel.
Each of the aforementioned patents are herein incorporated in there entirety by reference.
There is a need, therefore, in the art for an improved apparatus for injecting secondary fuel of various size pieces into the combustion zone of a kiln in a controlled and uniform manner. Moreover, there is a need in the art for an apparatus for injecting secondary fuel a distance which provides the fuel with ample time to burn and without the inlet of excessive amounts of air.